The invention relates to a safety belt pretensioner for safety belt systems in vehicles in which the belt buckle is arranged on a vehicle seat and the belt pretensioner engages said buckle, comprising a vehicle-sensitive sensor mass which is movably mounted on the vehicle seat and a drive activatable by the vehicle-sensitive movement thereof.
When attaching a belt pretensioner directly to a vehicle seat it is desirable to arrange the vehicle-sensitive trigger mechanism on the vehicle seat as well to avoid the necessity of complicated cabling between the vehicle bodywork and the vehicle seat displaceable relatively thereto. However, the sensor mass of the trigger mechanism is then subjected not only to the vehicle deceleration but also to decelerations which can occur on any seat adjustment. Under unfavourable conditions, for example sudden abrupt braking of the vehicle during execution of a seat adjustment, the forward movement of the seat in its guide rails being abruptly blocked at a detent, the trigger threshold of the vehicle-sensitive trigger mechanism may be exceeded and the belt tightening activated. The attempt to prevent activation of the belt pretensioner in such a case by blocking the sensor mass of the trigger mechanism whilst the grip for seat unlocking is actuated is not always successful because the abrupt deceleration at the vehicle seat can occur after the grip has been released again.